Artificial satellite with an orbit having a long staying time in a zenith direction, an orbit control method and a communication system therewith

ABSTRACT

A communication terminal for communicating through an artificial satellite, wherein the artificial satellite is placed into an orbit in which an individual satellite orbits on an elliptical orbit so that at least one of the artificial satellites is always viewable within a pre-defined range of operational elevational angle in a zenith direction from a service area. A group of the artificial satellites are satellites on respective orbits obtained by combining an inclination angle and an eccentricity squared of said elliptical orbit so that a time period during which an artificial satellite is viewable from ground is substantially identical and the communication terminal has a transmitter and receiver for transmitting and receiving a signal through the group of artificial satellites.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. application Ser. No. 09/081,551, filed May20, 1998, now U.S. Pat. No. 6,352,222 the subject matter of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates specifically to an artificial satellite,which is usable in the field of communications, such as satellitecommunications and mobile communications, a satellite orbit controlmethod and a communication system using the satellite.

There is a requirement to transfer medical information including imagedata, for an emergency case carried on an ambulance from the ambulanceto a paramedic center, and to direct medical treatment suitable for theemergency case to the ambulance from the doctors on duty at theparamedic center.

However, in the case of trying to transfer large-sized data, like imagefiles, satisfactory results can not obtained by the conventionalground-base communication infrastructure. In addition, in case ofcommunicating via geostationary satellites currently in service and/ormobile communication satellites to be deployed in the future, it isdifficult to establish stable and continuous transfer lines extendedfrom moving bodies because of shielding objects such as buildingstructures and trees.

Though it is certainly possible to transfer large-sized data frommovable objects, like an automobile, by using satellites moving in aspecific orbit, no definite method for defining such an orbit has beenestablished to date. Therefore, the orbit-related elements of such aspecific orbit have not been definitely identified as yet.

Conventional technologies and their problems are described below indetail.

(A) Technologies and Problems in Existing Communication Infrastructures

(A-1) Technologies and Problems in Ground-base CommunicationInfrastructures

In a case where large-sized data, like image files, are transferred fromthe movable bodies like automobile to a ground-base fixed station,communication methods via ground-base communication infrastructures orcommunication satellites can be considered. However, existingcommunication methods may not satisfy all the requirements for thesystem specification and performance.

Now, let's take as an example an ambulance. For carrying an emergencycase by ambulance, the average carrying time period is about 27 minutes.For serious cases, there occurs many instances in which the emergencycase may die if adequate medical treatment is not applied in time, whichis a strong motivation for the medical specialist to apply medicaltreatment to the emergency case in the ambulance or to suggest anadequate method for medical treatment to the emergency case to theemergency medical technician in the ambulance. However, about 15,000 ormore medical doctors would be required for paramedic services in orderto dispatch medical doctors with shift work to the about 5,000ambulances in Japan. However, this is not realistic, and so it isconsidered to be more effective to communicate adequate methods formedical treatment from the paramedic center to the ambulance. However,in the conventional ground-base communication systems, communicationlines with phone-level quality with which an instantaneous break mayoccur frequently are only available, and therefore, adequate methods forthe medical treatment can not be directed satisfactorily from theparamedic center. If image information captured by endoscope,electrocardiogram, echo and camera could be directly transferred to theparamedic center, it is supposed that satisfactory diagnosis anddirections for medical treatment of the emergency case could be given.However, ground-base communication infrastructures have such problems aslimitation of transmission band, limitation of communication coverageareas, cross talk and interference due to reflection by man-madebuilding structures, and so can not be applied to practical use for sucha purpose.

Similarly, though many requests exist for large-scale data transmissionfrom movable bodies, for example, live telecast of a marathon, theconventional ground-base communication infrastructure can not be usedfor this application.

(A-2) Technologies and Problems in a Geostationary CommunicationSatellite System

In the field of satellite communications using artificial satellites,communication systems using geostationary satellites and low-to-middlealtitude orbits are well known. There are the following problems inconventional communication satellites.

As a geostationary satellite has about a 24-hour orbit cycle almostequal to the earth's rotation cycle, the geostationary satellite can beviewed from the ground to be stationary at a point above the Equator.However, the elevation angle of such a geostationary satellite is low,for example, the elevation angle at Tokyo is at most 45 degrees even incase of good conditions. As the movable bodies in metropolitan areasmove on the roads surrounded by artificial building structures androadside trees, the lower range of the elevation angle is blocked bythose obstacles, and satellite communications with geostationarysatellites may be blocked. As the stationary satellites can be seen inan east-south to west-south direction, though communication lines can beestablished in a case where the movable body moves in a north-to-southdirection and a broader visual field to the satellite can be obtained,communication lines may be blocked by building structures and roadsidetrees at almost any time in a day in a case where the movable body movesin an east-to-west direction, especially, in a west direction.Therefore, satellite communications using qeostationary satellites donot produce satisfactory results for service in not-plain areas, like ametropolitan area and a mountain area.

(B) Technologies and Problems of Satellite Communication SystemsCurrently Under R&D

In the case of satellite communication systems using low-to-middlealtitude orbits, such as Iridium and Odyssey currently under developmentfor the purpose of cellular phone services using mobile communicationsatellites, the duration of time while the satellite in service stayswithin a high elevation angle range and comes in sight from the groundis generally short due to the limitation on the number of orbital planesfor the satellite and the number of satellites in service. Especially,since a satellite flying on the low altitude orbit has about 90 to 100minutes in its orbit cycle, the duration of time while the satellitestays within a high elevation angle range as viewed from the ground isas short as a few minutes. Therefore, when trying to use or apply thiskind of satellite communication systems for the purpose of stable anddefinite communication for large-scale data, as used in the aboveexample of an ambulance and a paramedic service system, without anyinfluence by building structures, plants and natural topographicfeatures over a certain extended time period, for example, more than 27minutes, it is required to configure such a system using pluralsatellites which alternately may come in sight at a higher elevationangle. In this case, some thousand or more satellites are required,which causes difficulties in procuring a number of satellites, theoperation thereof and launching cost reduction, and so this plan is notpractical also from an economical point of view.

In the case where a higher elevation angle is required, as in the aboveexample, conventional geostationary satellites for practical use andlow-to-middle altitude satellites currently under development are notfully applicable.

(C) Technologies and Problems in a Satellite Communication SystemCurrently Under Study

For example, as found in research reports, such as “Feasibility ofMobile Communication Mission Using NonGeostationary Satellite Orbits”,Technical Research Report, Japanese Electronics, Information andCommunication Society, Vol. 89, No.57, satellite communication systemscurrently understudy are discussed. Especially, an oblong orbit having alarger eccentricity squared is proposed in some research reportsincluding the above report.

According to Kepler's Law, an object passing around the apogee point ofthe orbit slows down. By defining an orbit having its apogee pointlocated on the upper air of the target service area, the duration timeduring which the satellite on this orbit stays at a high elevation anglecan be taken to be long enough. Therefore, it is necessary to use anoblong orbit in order to establish communication lines for a extendedperiod of time without a communication break due to building structures,roadside trees and natural geographical conditions.

As an example of oblong orbits, the Molnia orbit having about a 12-hourorbit cycle, a perigee altitude of some hundred km and an orbitalinclination angle of about 63.4 degrees has been practically used as anorbit for communication satellites and military satellites in Russianterritory since the 1960's. Though this orbit is a stable orbit with itsargument of perigee being fixed, and is certainly practical for serviceat the higher latitude locations over the Russian territory extended ina north and south direction, this orbit is not so practical for serviceat the lower latitude locations extended in a north and south direction,such as over Japan. Some orbits having about an 8-hour orbit cycle,about a 12-hour orbit cycle and about a 24-hour orbit cycle are proposedfor the services provided in the Japanese territory. However, thoseproposed orbits are designed with localized optimization, and, as theorbits suitable for the north-to-south and east-to-west extension of theJapanese territory, there has not been any proposal for optimizedorbits, methods for defining those orbits and definite operationtechnologies. This is because the design methodology for definition of asatellite orbit has been empirical in order to determine sixorbit-related elements.

There are various methodologies for identifying and defining orbits, butthe following six orbit-related elements are mainly used. Those aredefined for an individual reference time.

Semi-Major Axis a: semi-major axis of the ellipse (noted by symbol 54 inFIG. 5),

Eccentricity Squared e: flatness of the ellipse orbital

Inclination Angle I: angle defined between the orbital plane and theequational plate

Right Ascension of North-Bound Node Ω: angle (shown by symbol 63 in FIG.6) measured in the east direction from the vernal equinoctial point tothe crossing point of the orbit from the northern hemisphere to thesouthern hemisphere with the equational plate (this crossing point shownby symbol 62 shown in FIG. 6)

(0 degree≦Ω≦360 degrees)

Argument of Perigee ω: angle measured between the perigee and the rightascension of north-bound node 62 on the orbital plane (shown by symbol63 in FIG. 6)

(0 degree≦ω≦360 degrees)

True Anomaly θ: angle defined by the line connected between the perigeeand the focal point of the ellipse and the line connected between thesatellite and the focal point of the ellipse (shown by symbol 58 in FIG.5)

(0 degrees≦θ≦360 degrees).

The geometrical relationship for those elements will be described withreference to FIGS. 5 and 6. The satellite 51 moves on the ellipticalorbit having a focal point 50. The distance between the perigee 53 ofthe ellipse and the focal point 50 of the ellipse is represented byperigee radius Rp and with symbol 57 in FIG. 5. The distance between theapogee 52 of the ellipse and the focal point 50 of the ellipse isrepresented by apogee radius Ra and with symbol 56 in FIG. 5. Perigeeradius, apogee radius, semi-major axis a represented by symbol 54 inFIG. 5, semi-minor axis b represented by symbol 55 in FIG. 5 and theeccentricity squared e have the following relations.

Rp=a(1−e)

 Ra=a(1+e)

B=a(1−e ²)1/2

e=(Ra−Rp)/(Ra+Rp)

In FIG. 6, what is shown is an example in which the earth 60 ispositioned at the focal point of the elliptical orbit. The ellipticalorbit crosses at the north-bound node 62 on the equational plate fromthe southern hemisphere to the northern hemisphere, while the perigee ispositioned at the point 65 and the apogee is positioned at the point 66.The angle 64 between the equational plate 61 and the orbital planedefines the orbital inclination angle i. The right ascension of thenorth-bound node is defined by the angle 68 measured in the easterndirection from the vernal equinoctial point, and the argument of theperigee is defined by the angle 63 between the north-bound node 62 andthe perigee 65.

Even if the semi-major axis can be specified definitely by the orbitcycle, other major parameters may be determined to be arbitrary values,such as the eccentricity squared is an arbitrary real number 0.0 or overand less than 1.0, the orbital inclination angle is an arbitrary realnumber 0.0 degree or over and 180 degrees or smaller, and the argumentof perigee is an arbitrary real number 0.0 degree or over and 360degrees or smaller. Thus, there may occur a situation in which adesigner is forced to determine values for those parameters intuitivelyand/or empirically from his or her experiences.

If a satellite which can come in sight in the zenith direction for anextended period of time on the upper air of the target service area canbe realized, “large-scale data transfer from mobile bodies for anextended period of time” can be established by satellite communications.Thus, what has been sought are feasible methodologies for definingorbit-related elements and their definite values which can be adaptiveto Japanese territory characteristics and are cost-effective, that is,configured with less number of satellites forming the overall system.

As described above, in order to transfer large-scale data includingimage files from movable bodies, like an automobile, for an extendedperiod of time, it is required to make the satellite remain on the orbitin the zenith direction as long as possible and to communicate with thesatellite.

It has been generally recognized that it is preferable to establish anorbit shaped in an oblong ellipse having its apogee on the upper air ofthe target service area, in order to satisfy the above describedrequirement. However, adequate methodologies and algorithms for definingorbit-related elements have not been proposed. In addition, there is nodefinite proposal for specified values for those parameters to beoptimized for the services over the whole Japanese land.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a specific methodologyfor setting orbit-related parameters with respect to the above describedproblems, and to set the orbit-related parameters in terms of a limitedrange for the parameters obtained by this methodology.

Another object of the present invention is to provide various systemsusing artificial satellites arranged so as to be able to remain insightin the zenith direction for a long stretch of time in order to solve theabove described problems.

And furthermore, another object of the present invention is to providean orbit control means for performing the control of artificialsatellite orbits based on the orbit-related parameters defined in themanner described above.

In order to achieve the above objects, in accordance with the presentinvention, in an artificial satellite traveling along an ellipticalorbit, the elliptical orbit is defined by six orbit-related parametersobtained with input conditions, including the geographical condition ofthe service area to be covered by the artificial satellite, thetolerance of the ascending vertical angle within which the artificialsatellite can be viewed from the service area, and the reference timedefining the orbit elements.

The artificial satellite traveling on an elliptical orbit according tothe present invention travels on such an oblong orbit that theartificial satellite may come in sight at an angle larger than themaximum elevation angle with which the geostationary artificialsatellite is viewed from the service area corresponding to theartificial satellite.

As for the determination of orbit elements, six orbit related parametersare determined by steps including the step of setting the semi-majoraxis, the step of setting the perigee arguments, the step of setting thesemi-vertical angle, the step of setting the desired service time, thestep of setting the polygon including the service area, the step ofsetting the number of artificial satellites, the right ascension of thenorth-bound node of the individual artificial satellite and the trueanomaly of the individual artificial satellite, the step of setting theinitial value for the orbital inclination angle, the step of calculatingthe duration time for the artificial satellite coming into sight fromthe individual apex of the polygon, the step of setting the combinationof the orbital inclination angle and the eccentricity squared and thestep of resetting the right ascension of the north-bound node and trueanomaly of the individual artificial satellite.

In order to achieve the above described object of the present invention,in the group of artificial satellites including plural artificialsatellites traveling on elliptical orbits, six orbit-related parametersof the elliptical orbits of the individual artificial satellites areobtained with input conditions including the geographical condition ofthe service area to be covered by the artificial satellites, thetolerance of the ascending vertical angle within which any one of thegroup of artificial satellites can be viewed from the service area, andthe reference time defining the orbit elements; and, what are used are agroup of satellites such that one or more artificial satellites arearranged on the individual orbital planes within the predetermined rangeof the ascending vertical angle viewed in the zenith direction from theservice area by combining plural elliptical orbits so that at least oneor more artificial satellites can always come in sight.

In order to achieve the above described object of the present invention,artificial satellites with orbits provided by the present invention areused in various systems using artificial satellites, such as an orbitcontrol system for controlling the orbit of satellites, a satellitecommunication system for conducting satellite communications withartificial satellites, and an earth observing system using artificialsatellites carrying earth observing devices.

In case the satellite communication terminal in the satellitecommunication system is used within the service area covered by theartificial satellites of the present invention, the satellitecommunication terminal may have send/receive means for sending andreceiving signals to and from the target artificial satellite coming insight in the range of the ascending vertical angle in the predeterminedzenith direction, and may be loaded on the movable body moving mainlywithin the service area. In addition, the satellite communicationterminal may include GPS means for receiving radio waves from GPSsatellites forming a global positioning system and at least formeasuring the position of the satellite communication terminal itself,and may have measuring means for measuring the quantity consumed byevery house to be charged for electricity, gas or public water suppliedby public utility services.

In order to achieve the above described object of the present invention,in the group of artificial satellites including plural artificialsatellites traveling in elliptical orbits, six orbit-related parametersof the elliptical orbits of the individual artificial satellites areobtained so as to satisfy the input conditions including thegeographical condition of the service area to be covered by theartificial satellites, the tolerance of the ascending vertical anglewithin which any one of the group of artificial satellites can be viewedfrom the service area, and the reference time defining the orbitelements. In case plural artificial satellites are employed, one or moreartificial satellites may be arranged on the individual orbital planeswithin the predetermined range of ascending vertical angle viewed in thezenith direction from the service area by combining plural ellipticalorbits so that at least one or more artificial satellites can alwayscome in sight.

The above described object is established by a orbit elementdetermination apparatus comprising means for setting a polygon includinga semi-major axis, a perigee argument, a semi-vertical angle, a servicetime and a service area; means for setting the number of satellite andright ascension of the north-bound node and true anomaly of theindividual satellite; means for setting the initial value for theorbital inclination angle; means for calculating the duration time forthe satellite coming into sight from each apex of the polygon; means forsetting a combination of the orbital inclination angle and theeccentricity squared and means for resetting the right ascension of thenorth-bound node and the true anomaly of the individual satellite.

In order to achieve the above described object, in the satellitecommunication system for conducting satellite communications withartificial satellites, the present invention at least includes anartificial satellite, a satellite communication terminal for conductingsatellite communications with artificial satellites and a base stationfor conducting communications to and from the satellite communicationterminal with the artificial satellites, in which the artificialsatellite is a satellite that travels on such an oblong orbit that theartificial satellite may come in sight at an angle larger than themaximum elevation angle with which the geostationary artificialsatellite is viewed from the service area corresponding to theartificial satellite, and the satellite communication terminal may beloaded on a movable body and have send/receive means for sending andreceiving signals to and from the target artificial satellite coming insight in the range of the ascending vertical angle in the predeterminedzenith direction when used within the service area covered by theartificial satellite.

In order to achieve the above described object, in the satellitecommunication system for conducting satellite communications withartificial satellites, the present invention at least has an artificialsatellite and plural satellite communication terminals for conductingsatellite communications with artificial satellites, in which theartificial satellite is a satellite that travels on such an oblong orbitthat the artificial satellite may come in sight at an angle larger thanthe maximum-elevation angle with which the geostationary artificialsatellite is viewed from the service area corresponding to theartificial satellite, and plural satellite communication terminals havesend/receive means for sending and receiving signals to and from anothersatellite communication terminal, and at least one of the pluralsatellite communication terminals is located within the main servicearea, the other of the plural satellite communication terminals arelocated in the area outside the main service area and from whichsatellite communications with the artificial satellite are possible, andany one of the relay operations may be selected in response to theascending vertical angle of the artificial satellite viewed from themain service area covered by the artificial satellite, in which relayoperations include a relay operation between satellite communicationterminals located within the main service area, a relay operationbetween the satellite communication terminal located within the mainservice area and the satellite communication terminal located in theother areas, and a relay operation between satellite communicationterminals located in the area other than the main service area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart representing the method for setting sixorbit-related parameters which make it possible to sight the artificialsatellite in the zenith direction over an extended time period inaccordance with the present invention.

FIG. 2 is a diagram illustrating the information flow for controllingthe orbit of the artificial satellite in compliance with sixorbit-related parameters set by the algorithm of the present invention.

FIG. 3 is a diagram illustrating the information flow in the tasksperformed in the artificial satellite operation control apparatus fororbit control of the artificial satellite.

FIG. 4 is a diagram illustrating the process and information flow in theartificial satellite for orbit control of the artificial satellite.

FIG. 5 is a geometrical diagram of six orbit-related parameters definingthe shape of the orbit, in which the orbit is viewed in the normaldirection to the orbital plane.

FIG. 6 is a geometrical diagram of six orbit-related parameters definingthe shape of the orbit, in which the orbit and the earth are shown inbird's eye view.

FIG. 7 is a bird's-eye view of the earth showing the necessity forsetting six orbit-related parameters by considering the service area.

FIG. 8 is a mapping diagram of the artificial satellite orbit onto theground in which the artificial satellite has about 24-hour circumvolantflight with eccentricity squared being 0.25, orbital inclination anglebeing 55 degrees and perigee argument being 270 degrees, and themappemonde is based on isometric projection with respect to latitude andlongitudinal measures.

FIG. 9 is a mapping diagram of the artificial satellite orbit onto theground in which the artificial satellite has about a 24-hourcircumvolant flight with eccentricity squared being 0.38, orbitalinclination angle being 45 degrees and perigee argument being 270degrees, and the mappemonde is based on isometric projection withrespect to latitude and longitudinal measures.

FIG. 10 is a map based on isometric projection with respect to latitudeand longitudinal measures, which includes a ground-mapping orbit 82 ofthe artificial satellite with about 24-hour circumvolant flight witheccentricity squared being 0.35, orbital inclination angle being 63.4degrees and perigee argument being 270 degrees, and a ground-mappingorbit 83 having the same orbital period, eccentricity squared,inclination angle and perigee argument as those of the ground-mappingorbit 82 in which the right ascension of a north-bound node is sodefined as to obtain a ground-mapping orbit overlapping exactly theground-mapping orbit 82.

FIG. 11 is a diagram showing the orbit around the earth with respect tothe orbit configuration example 1 obtained by the algorithm of thepresent invention.

FIG. 12 is a diagram showing the orbit around the earth with respect tothe orbit configuration example 2 obtained by the algorithm of thepresent invention.

FIG. 13 is a block diagram showing an application example of a mobiletelephone system.

FIG. 14 is a diagram showing an example o f the system mainly for theimage transmission from a mobile object like an ambulance.

FIG. 15 is a diagram showing an example of a rescue system used inmountain or ocean areas.

FIG. 16 is a diagram showing an example of an automated accountingsystem for public utility charges.

FIG. 17 is a diagram showing another example of a system used mainly forimage transmission from a movable body like an ambulance.

FIG. 18 is a diagram showing an example of a system for dispatchingprograms to a plurality of movable bodies.

FIG. 19 is a block diagram showing an example of a mobile communicationsystem for the system shown in FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, embodiments related to the following items in accordance with thepresent invention will be described in detail below:

(a) method (algorithm) for setting optimal orbit elements;

(b) operation for setting optimal orbit elements by applying thealgorithm; and

(c) strategy for implementing the optimal orbit elements and controllingsatellites.

(1) Method for Setting Optimal Orbit Elements (Algorithm)

In order to make an artificial satellite come in sight in the zenithdirection in such a way that the artificial satellite may not be blockedfrom sight by man-made building structures, plants and naturaltopographic features, it is effective to use elliptical orbits havingtheir apogee in the upper air of the observation area. A method forsetting orbit elements will be described below. This setting method isillustrated schematically by the flowchart shown in FIG. 1.

(1-1) Setting Semi-major Axis (Step 4)

In considering the operation of the satellite itself and the operationof the satellite communication using the satellite, by using orbits onwhich the satellite travels with a circumvolant period equal to theproduct of any whole number and a time period of a single day orquotient of a time period of a single day and any whole number, anidentical satellite can be made to come in sight in a designateddirection at a definite time in a day, and therefore, a periodicoperation of the satellite can be established. Table 1 shows the resultof analysis of the duration time for the satellite coming in sight andits occurrence in a day, in which the orbital period is assumed to beone of 4, 6, 8, 12, 16, 24, 32 and 36 hours.

TABLE 1 Cycle (Hour) 4 6 8 12 16 24 32 36 Sapporo 0:25 1:30 1:40 6:011:51 8:23 2:25 2:48 Sendai 0:34 1:14 1:15 3:56 1:16 6:56 1:44 1:49 Tokyo0:36 1:11 1:04 3:15 1:03 6:26 1:29 1:06 Niigata 0:37 1:15 1:12 3:49 1:136:53 1:41 1:32 Nagoya 0:37 1:11 1:01 3:05 0:59 6:20 1:25 1:07 Osaka 0:371:07 0:59 2:54 0:55 6:12 1:20 1:07 Hiroshima 0:36 1:01 0:54 2:37 0:515:57 1:08 1:09 Kouchi 0:36 1:01 0:53 2:34 0:50 5:54 1:06 1:06 Fukuka0:30 0:52 0:49 2:16 0:45 5:38 0:50 1:08 Naha 0:17 0:33 0:30 0:57 0:233:30 0:43 0:54 Visible 1-2 1-2 1 2 1/2 2 1/4- 1/3- Occurrence (/ 1/2 2/3Day)

Table 1 shows the duration times during which a satellite on the orbitswith their orbital inclination angle being 63.4 may come in sight in thezenith direction with an elevation angle of more than 70. In terms of asystem configuration, it is advantageous to select the satellites onorbits having orbital periods of 12 hours or 24 hours. Thus, what can beconcluded is that the orbits specifically having orbital periods of 12hours or 24 hours are practical even if the orbital inclination anglechanges. From the period of the satellite, the semi-major axis 11 isdetermined uniquely to be about 26,562 km for an orbit having about a12-hour orbital period or to be about 42,178 km for an orbit havingabout a 24-hour orbital period.

(1-2) Setting Perigee Argument (Step 5)

The perigee argument 12 depends on the location of the service area inwhich the communication service or the earth observing service can bemade available by using satellites. In a case where the service area islocated in the Northern hemisphere, the perigee argument is determinedto be about 270 degrees so that the perigee may be located in the upperair of the Northern hemisphere. In a similar manner, in a case where theservice area is located in the Southern hemisphere, the perigee argumentis determined to be about 90 degrees. Those conditions are necessary forlocating the apogee in the upper air of the service area. (1-3) Settingeccentricity squared, orbital inclination angle, north-bound node andtrue anomaly.

(a) Setting Semi-vertical Angle (Step 1)

As the term “zenith direction” still represents a qualitative property,a semi-vertical angle is so defined as to be in an allowable angle rangewithin which the satellite will come in sight, such as 20 degrees or 40degrees. In this case, the corresponding elevation angle is 70 degreesor 50 degrees, respectively. The satellite can come in sight over anextended time period while being located within a circular cone withthis semi-vertical angle extended in the central axis relative to thezenith. The smaller the semi-vertical angle, the larger will be thenumber of satellites required for service.

(b) Setting Required Service Time (Step 2)

The duration of the service time for which the satellite service needsto be available should be defined. For example, in the case of anambulance dispatch service, 24-hour service is required.

(c) Setting Polygon Including Service Area (Step 3)

As the conventional geostationary satellite can be seen as at astandstill in the sky, the communication to the satellite can beestablished by transmitting a beam between the satellite and the servicearea. In Iridium and Odyssey systems using low-to-middle altitudeorbits, since they use a design concept wherein a number of satellitescover all the service areas on the ground, there is no need for managingthe individual service areas with their own characteristics. As for theelliptical orbits to be used by the present invention, the satellites onthe elliptical orbits can not be seen to be at a standstill from theground, and hence, it is desirable that the number of satellites issmall. Thus, the locus of orbits should be selected so as to beoptimized for the individual service areas.

In accordance with the present invention, the latitude, longitude andelevation of four locations, including northernmost, southernmost,westernmost and easternmost portions of the service area, are defined.In case the service area is over the Japanese archipelago, the locationsshown in Table 2 are considered as northernmost, southernmost,westernmost and easternmost.

TABLE 2 North South Place Location Latitude Latitude NorthernmostEtorofu Island 45 33.3′ 148 45.5′ Easternmost Minamitorishima 24 17.0′153 59.2′ Southernmost Okinotorishima 20 25.3′ 136 4.9′ WesternmostYonakunijima 24 26.6′ 122 56.0′

Those four locations are as shown in FIG. 7 and their altitude andlongitude do not take an identical value generally. In case some servicearea is not included in a quadrangle having those locations at itscorners, additional locations with their own latitude, longitude andelevation are defined so as to form such a polygon that includes all theservice areas. This polygon can be formed by plural adjoining triangles.

Steps (a) to (c) can be performed in random order.

(d) Setting the Number of Satellites, the Right Ascension of theNorth-bound Node and a True Anomaly of an Individual Satellite (Step 6)

In a case where 24-hour service is attempted to continue with anelliptical orbit, it is apparent that a single satellite can not realizethis service. Therefore, in order to use 2 or more satellites forestablishing the necessary system configuration, the number ofsatellites to be used is defined. In order to establish a continuousservice in a service area, it is effective to allocate a singlesatellite on a single orbital plane. In addition, it is desirable tomake the shape or trajectory of the individual orbits identical. Theright ascension of the north-bound node is shifted from one orbit toanother orbit by an angle equal to the division of 360 degrees by thenumber of satellites. For example, assuming that the number ofsatellites is three, the individual satellites travel on the orbits withtheir right ascension of the north-bound node shifted by 120 degrees.

The right ascension of the north-bound node rotates with a constantinterval around the earth's axis due to the gravitational potential ofthe earth. This means that the orbital plane rotates around the earth'saxis. Therefore, it is required to define the right ascension ofnorth-bound node at the reference time so that the apogee may be locatedin the upper air of the service area. In this step, it is possible togive an arbitrary value to the right ascension of the north-bound nodefor the convenience of analysis. In addition, it is possible to set anarbitrary value on the inertial space of the service area for theconvenience of analysis.

In setting the true anomaly, in case one satellite is located at theperigee on the orbit, the true anomaly of the other satellite may beshifted by an angle corresponding to the division of the orbital periodof the satellite by the number of satellites in the system. For example,in a case of three satellites, the true anomaly of the individualsatellite adjacent to each other may be shifted each by an anglecorresponding to ⅓ of the orbital period.

By setting the right ascension of the north-bound node and the trueanomaly of the individual satellites, their orbits as mapped on theground become identical and they come in sight on the upper air of acommon area.

(e) Setting Initial Value of Orbital Inclination Angle (Step 7)

It is supposed to make it possible to provide almost uniform service inthe whole service area if the apogee of the orbit is located in theupper air of the center of mass of this polygon. However, because of themovement of the position on the ground due to earth rotation and therelative movement of the satellite traveling on the orbit, thisconfiguration of orbits is not necessarily ideal. Therefore, using aninitial value for the orbital inclination angle equal to the latitude ofthe position near the center of mass of the polygon, the analysis isperformed in the following manner.

(f) Calculating the Duration Time for a Satellite Coming into Sight froman Individual Apex of the Polygon (Steps 8 and 9)

So far, the initial values for the semi-major axis 11, the argument ofperigee 12, the right ascension of the north-bound node, the trueanomaly and the orbital inclination angle of the individual orbits weredetermined. Five elements out of six orbit-related parameters have beendetermined.

The duration time during which the individual satellite can be viewedfrom the individual apex of the polygon and within a circular cone withthis semi-vertical angle extended in the central axis to the zenith iscalculated for the individual satellite. This time can be obtained bygeometrical computation and Repler's laws of planetary motion, orcalculated by numerical calculation by computers. As shown in Step 8 ofFIG. 1, by changing the eccentricity squared, from 0.0 to 1.0, the rangeof the eccentricity squared with which the duration times for thesatellite to be viewable from all the apexes of the polygon are almostidentical to one another, is calculated. In case of using computers, itis possible to use a method in which the individual duration times fromthe individual apexes of the polygon are compared with one another byincrementing the eccentricity squared with a definite difference.

Next, as shown in Step 9 of FIG. 1, by varying the orbital inclinationangle and the eccentricity squared from their initial values, the rangeof the eccentricity squared, with which the duration times for thesatellite to be viewable from all the apexes of the polygon are almostidentical to one another, is calculated. Similarly, in the case of usingcomputers, the individual duration times from the individual apexes ofthe polygon are compared with one another by incrementing the orbitalinclination angle with a definite difference. By defining the referencetime and fixing the right ascension of the north-bound node and theposition on the inertial space of the service area, both correspondingto the reference time, and then, simulating the orbital calculation bycomputers in order to obtain the duration time for the satellite to beviewable, the duration time for all the satellites, during which theindividual satellite can be viewed from the individual apex of thepolygon and within a circular cone with this semi-vertical angleextended in the central axis to the zenith, can be obtained.

In this time, the time length during which the satellite stays withinthe semi-vertical angle is equivalent to the time length for which asingle satellite can occupy a service for a single orbital plane. Ifthis time length is so selected as to be a divisor of about 24 hours,that is, the earth's rotation period, for example, about 1 hour, about 2hours, about 3 hours, about 4 hours, about 6 hours, about 8 hours, about12 hours and about 24 hours, it is favorable for providing periodicservices and satellite operations. It is necessary to use at least onesatellite for providing 24-hour service, which means that the servicecan be continuously available all day long, and to use at least twosatellites for providing 12-hour service, respectively. Therefore, ifnecessary, the number of satellites to be required can be defined againby going back to the above described process (d) (Step 6).

(g) Setting a Combination of the Orbital Inclination Angle and theEccentricity Squared

By repeating the analysis in Steps 8 and 9, the combination of theorbital inclination and the eccentricity squared for providing uniformservices in an arbitrary position in the polygon including the servicearea can be obtained in terms of the numerical ranges shown in theblocks 13 and 14 of FIG. 1.

(h) Resetting the Right Ascension of the North-bound Node and the TrueAnomaly (Step 10)

In the last step, the reference time is defined so as to be tuned to thetime for launching the satellite, and the corresponding right ascensionof the north-bound node 15 and the true anomaly 16 may be determinedproperly.

All or partial processes of the above described algorithm can begenerated as programs and may be executed by computers. For example, itis possible to use a system in which, after users input the data atSteps 1 to 5, the computer executes the programs corresponding to Steps6 to 10 in response to the input data and conditions.

(2) Setting Orbit-related Elements by the Above Described Algorithm

(2-1) In Case of Defining the Service Area as in Japan

By using the above described algorithm, for the service area includingall the Japanese territory, an elliptical orbit having the orbit-relatedelements shown in Case 2 of Table 3 can be obtained as a combination ofranges of orbit-related elements so that a single satellite may come insight for about 12 hours a day from all the Japanese territory in thezenith direction at an elevation angle of more than 55 degrees. In thiscase, if a couple of satellites are arranged so that their rightascensions of the north-bound node may be shifted by 180 degrees andtheir true anomaly may be shifted by 180 degrees corresponding to halftime of the orbit cycle, the satellite can come in sight for 24 hours aday from all the Japanese territory in the zenith direction at anelevation angle of more than 55 degrees.

In case of considering the Japanese territory excluding isolatedsouthern islands like Okinotori Island and Minamitori Island, byshifting the right ascensions of the north-bound node of four satellitesindividually by 90 degrees and using the elliptical orbit having theorbit-related elements shown in Case 1 of Table 3, either of foursatellites can always come in sight in the zenith direction an elevationangle of more than 55 degrees.

TABLE 3 Item Value Case ID Case 1 Case 2 Semi-Major Axis approximatelyapproximately (km) 42,178 42,178 Eccentricity approximately 0.24approximately Squared or larger and 01.24 or larger approximately 0.38and approximately or smaller 0.38 or smaller Orbital approximately 35 orapproximately 47 Inclination Angle larger and or larger and (degree)approximately 40 or approximately 52 smaller, or or smaller, orapproximately 140 approximately 128 or larger and or larger andapproximately 155 approximately 133 or smaller or smaller Argument ofapproximately 90 or approximately 90 Perigee (degree) approximately 270or approximately 270 Right Ascension of value set in value set inNorth-Bound Node responsive to the responsive to the (degree) referencetime when reference time defining orbit- when defining related elementsorbit-related elements True Anomaly value set in value set in (degree)or a responsive to the responsive to the position on the reference timewhen reference time orbit at a defining orbit- when defining specifiedtime related elements orbit-related elements

The orbit of an artificial satellite, if a short cycle or long cycle,always fluctuates under the influence of the earth's gravitational fieldand the attractive force of the Moon and Sun, and is controlled withsome tolerance to a certain extent. For this reason, approximate valuesor target nominal values after orbit control are shown in theorbit-related elements mentioned in this embodiment and accompaniedtables.

In a case where the orbit cycle is about 12 hours, for the locations inHokkaido, Honshu, Shikoku, Kyushu and Okinawa, the elliptical orbitshaving orbit-related elements shown in Case 3 of Table 4 are obtained asa combination of orbit-related elements which enables the satellites tocome insight during about 6 hours in the zenith direction at anelevation angle of more than 70 degrees.

TABLE 4 Item Value Case ID Case 3 Semi-Major Axis (km) approximately26,562 Eccentricity Squared approximately 0.70 or larger andapproximately 0.80 or smaller Orbital Inclination Angle approximately 30or larger (degree) and approximately 45 or smaller, or approximately 135or larger and approximately 150 or smaller Argument of Perigee (degree)approximately 90 or approximately 270 Right Ascension of North- valueset in responsive to Bound Node (degree) the reference time whendefining orbit-related elements True Anomaly (degree) or a value set inresponsive to position on the orbit at a the reference time whenspecified time defining orbit-related elements

In the case of selecting values for the orbit-related elements to beoutside the above described ranges, for example, in Case 2 where theorbit cycle is about 24 hours, there might be such a case where thesatellite can not come in sight in the zenith direction at an elevationangle of more than 55 degrees at some partial areas in Japan. Forexample, in case the orbital inclination angle is 45 degrees or smaller,or 135 degrees or larger, the service duration time for the northernmostareas in Japan may become less than 24 hours, but, in contrast, in casethe orbital inclination angle is between 55 degrees and 125 degrees, theservice duration time for the southernmost areas in Japan may becomeless than 24 hours. In case the eccentricity squared is about 0.25 orsmaller, the service duration time for the northernmost areas in Japanmay become less than 24 hours; and, in case the eccentricity squared isabout 0.38 or larger, the service duration time for the westernmost oreasternmost areas in Japan may become less than 24 hours. FIG. 8 shows aground-mapped trace of the orbit having about a 24-hour orbital cycle inwhich the eccentricity squared is 0.25, the orbital inclination angle is55 degrees and the argument of perigee is 270 degrees. FIG. 9 shows aground-mapped trace of the orbit having about a 24-hour orbital cycle inwhich the eccentricity squared is 0.38, the orbital inclination angle is45 degrees and the argument of perigee is 270 degrees. In case theorbital inclination angle is between 0 and 90 degrees, the larger theeccentricity squared, the wider the ground-mapped orbit extends in theeast and west directions. In this case, the larger the orbitalinclination angle, the wider the ground-mapped orbit extends in thenorth and south directions. In contrast, in case the orbital inclinationangle is between 90 and 180 degrees, the smaller the orbital inclinationangle, the wider the ground-mapped orbit extends in the north and southdirections. From ground-mapped orbits shown in FIGS. 8 and 9, it is wellunderstood that the service can not be fully provided at the assumedpositions if the values for the orbit-related elements go beyond thosedefined in such a manner as described above.

From the above description, the optimized ranges for the orbit-relatedelements for covering all service areas in Japan can be summarized inTable 5. As some examples, the service areas, tolerable elevation anglesand the number of satellites to be required are additionally tabulated.

TABLE 5 Orbit with approximately 12-hour cycle Orbit with approximately24-hour cycle Case ID Case 3 Case 1 Case 2 Case 4 Semi-majorapproximately approximately approximately approximately Axis (km) 26,56242,178 42,178 42,178 Eccentricity approximately approximatelyapproximately approximately Squared 0.70 or larger 0.24 or 0.24 orlarger 0.42 or larger and larger and and and approximately approximatelyapproximately approximately 0.80 or smaller 0.38 or smaller 0.38 or 0.48or smaller smaller Orbital approximately approximately approximatelyapproximately Inclination 30 or larger 35 or larger 47 or larger 62 orlarger Angle and and and and (degree) approximately approximatelyapproximately approximately 45 or smaller, 40 or smaller, 52 or smaller,66 or smaller, or or or or approximately approximately approximatelyapproximately 135 or larger 140 or larger 128 or larger 114 or largerand and and and approximately approximately approximately approximately150 or smaller 155 or smaller 133 or smaller 118 or smaller Argument ofapproximately approximately approximately approximately Perigee 90 or 90or 90 or 90 or (degree) approximately approximately approximatelyapproximately 270 270 270 270 Right value set in value set in value setin value set in Ascension of responsive to responsive to responsive toresponsive to North-Bound the reference the reference the reference thereference Node time when time when time when time when (degree) definingorbit- defining orbit- defining defining related related orbit-relatedorbit-related elements elements elements elements True Anomaly value setin value set in value set in value set in (degree) or responsive toresponsive to responsive to responsive to a position the reference thereference the reference the reference on the orbit time when time whentime when time when at a defining orbit- defining orbit- definingdefining specified related related orbit-related orbit-related timeelements elements elements elements Example Target Service WholeJapanese Whole Japanese Whole world Area land excluding land isolatedislands like Minamitorishima and Okinotorishima Tolerable 70 55 50Elevation Angle (unit: degree) Number of 3-4 2 36 Required Satellites

(2-2) Cases Assuming Services all over the World

In case the whole world is a target of services, the whole world is madeto be divided into sub areas, each having a constant dimension, and theabove described algorithm can be applied to the individual sub-areas.However, as for the areas near the Equator, there may be a case whereina geostationary orbit brings better results than the elliptical orbitdoes, and therefore, it is effective to combine the elliptical orbit andthe geostationary orbit in order to provide services all over the world.For example, by combining plural elliptical orbits having theorbit-related elements shown in FIG. 6 and geostationary satellites, thewhore world can be covered for providing cervices.

TABLE 6 Item Value Case ID Case 4 Semi-Major Axis (km) approximately42,178 Eccentricity Squared approximately 0.42 or larger andapproximately 0.48 or smaller Orbital Inclination Angle approximately 62or larger (degree) and approximately 66 or smaller, or approximately 144or larger and approximately 118 or smaller Argument of Perigee (degree)approximately 90 or approximately 270 Right Ascension of North- valueset in responsive to Bound Node (degree) the reference time whendefining orbit-related elements True Anomaly (degree) or a value set inresponsive to position on the orbit at a the reference time whenspecified time defining orbit-related elements

As described above, the ground-mapped orbit extends in the east and westdirections by making the value of the eccentricity squared larger, andthe ground-mapped orbit extends in the south and north directions bymaking the value of the orbital inclination angle larger. In this case,near the center part of the domain enveloped by the ground-mapped orbit,there occurs an area which can not obtain any service from thesatellite. This problem can be solved by arranging another orbit so thatits ground-mapped orbit may intersect its adjacent ground-mapped trace,as shown in FIG. 10.

(3) Method for Realizing the Defined Orbit-related Elements and forControlling the Satellite

The orbit of an artificial satellite having the orbit related elementsso defined as described above is controlled in the following manner.

As shown in FIG. 2, when launching the artificial satellite 20, theinformation relating to the six orbit-related elements determined inadvance to be suitable for the target service area is supplied to thelauncher operation control facility 21, from which the informationrelated to the target orbit parameters 22 is transferred to thelauncher. The launcher 23 launches the satellite onto the target orbitautomatically or in responsive to the control command from the launcheroperation control facility 21.

After the satellite 20 is launched onto the target orbit, theinformation related to six orbit-related elements 17 suitable for thetarget service area is periodically supplied to the satellite operationcontrol facility 18, and the information related to the control command19 is transferred to the satellite 20, and finally, the orbit of thesatellite 20 is controlled by the control system so as to trace thetarget orbit defined by the target six orbit-related elements.

As this orbit control method is compatible with conventional and generalorbit control methods, the details thereof will be described later.

Next, more detailed examples of the individual embodiments referred toabove will be described. In accordance with this invention, thefollowing two concepts form a 2-by-2 matrix context:

orbit-related elements and their ranges defined by the algorithm of thepresent invention, and

systems employing the satellites traveling on the orbits so defined.

These two concepts will be described separately. In addition, what willbe described is an operative example of the method for controlling thesatellite so as to trace the orbits with their six orbit relatedelements defined to be suitable for the target service area.

(4) Orbit-related Elements and their Range Obtained by the Algorithm inAccordance with the Present Invention

(4-1) Orbit Arrangement Example 1

In this embodiment, an example of orbit arrangement is directed toservices covering the whole Japanese territory. The orbit of anartificial satellite always fluctuates under the influence of theearth's gravitational field and the attractive forces produced by theMoon and Sun, and is controlled with some tolerance to a certain extent.For this reason, target nominal values after completing the orbitcontrol are shown for the orbit-related elements to be shown in theindividual examples of the orbit arrangement.

In the example of the orbit arrangement, there are two orbit planes asshown in FIG. 11, and the satellite 110 and the satellite 111 arearranged on separate orbits, respectively. The satellite 110 completesthe orbit 112 once in about 24 hours, and the satellite 111 completesthe orbit 113 once in about 24 hours. The orbit cycle of the satellites110 and 111 is about 24 hours, their eccentricity squared ranges between0.24 and 0.38, their orbital inclination angle ranges between 47 degreesand 52 degrees or between 128 degrees and 133 degrees, and theirargument of perigee is 270 degrees. As shown in FIG. 11, their rightascensions of north-bound node shift mutually by 180 degrees and aredefined so that their apogees may be located at a desired position abovethe Japanese territory. In terms of relative position between thesatellites on their own orbits, the satellite 111 is arranged to belocated at the apogee on the orbit 113, while the satellite 110 islocated at the perigee on the orbit 112. This orbit arrangement isobtained by the algorithm shown in FIG. 1 and is realized by the controlmethod shown in FIG. 2.

With this orbit arrangement, at any position in the whole of Japan,including the northernmost point, the southernmost point, theeasternmost point and the westernmost point, the satellite 110 or thesatellite 111 can come in sight always in the zenith direction with itselevation angle more than 55 degrees. As the satellite 110 and thesatellite 111 each have a 24-hour orbit cycle, the occurrence ofin-sight and out-of-sight positions of the satellite in the zenithdirection with its elevation angle more than 55 degrees is periodic andorderly. In this case, the satellite 110 and the satellite 111alternately come in sight and out of sight with about a 12-hour cycle,and their duration time for in-sight positions in the zenith directionwith its elevation angle more than 55 degrees is about 12 hours. Thereexists certainly a timing when both of the satellites 110 and 111 comein sight in the zenith direction with its elevation angle more than 55degrees. This timing comes once every day with a 24-hour cycle.

Thus, by using a satellite represented by the satellite 90 to thecommunication satellite in FIGS. 13 to 16, showing examples of systemsusing the orbit arrangement described above, it will be appreciated thata communication system without communication blackout due to shieldingand/or the presence of an obstacle can be achieved.

(4-2) Orbit Arrangement Example 2

In this embodiment, an example of an orbit arrangement directed toservices covering the whole Japanese territory is considered.

In the example of such an orbit arrangement, there are four orbitplanes, as shown in FIG. 12, and the satellite 120 a, the satellite 120b, the satellite 120 c and the satellite 120 d are arranged on separateorbits, respectively. The satellite 120 a travels on the orbit 121 a,the satellite 120 b travels on the orbit 121 b, the satellite 120 ctravels on the orbit 121 c and the satellite 120 d travels on the orbit121 d, each satellite completing its orbit in about 12 hours. The orbitcycle of the satellites 120 a, 120 b, 120 c and 120 d is about 12 hours,their eccentricity squared ranges between 0.70 and 0.80, their orbitalinclination angle ranges between 30 degrees and 45 degrees or between135 degrees and 150 degrees, and their argument of perigee is 270degrees. As shown in FIG. 12, their right ascensions of the north-boundnode shift mutually by 90 degrees, and are defined so that their apogeesmay be located at a desired position above the Japanese territory. Interms of relative position between the satellites on their own orbits,the satellite 120 b and the satellite 120 d are arranged to be locatedat the apogee on their corresponding orbits 121 b and 121 d,respectively, while the satellite 120 a and the satellite 120 c arelocated at the perigee on the orbits 121 a and 121 c.

With this orbit arrangement, at the areas in Hokkaido, Honshu, Shikokuand Kyuhu and Okinawa, the satellite 120 a, the satellite 120 b, thesatellite 120 c or the satellite 120 d can come in sight always in thezenith direction with its elevation angle more than 70 degrees. As thesatellite 120 a, the satellite 120 b, the satellite 120 c and thesatellite 120 d each have a 12-hour orbit cycle, the occurrence ofin-sight and out-of-sight positions of the satellite in the zenithdirection with its elevation angle more than 70 degrees is periodic andorderly. This orbit arrangement is obtained by the algorithm shown inFIG. 1, realized by the control method shown in FIG. 2. In this case,the satellite 120 a, the satellite 120 b, the satellite 120 c and thesatellite 120 d alternately come in sight and out of sight onceeveryday, and their duration time for an in-sight position in the zenithdirection with its elevation angle more than 70 degrees is about 6hours. Thus, either of those satellites can come in sight one afteranother all day long for 24 hours in the zenith direction with itselevation angle more than 70 degrees. There exists certainly a timingwhen all of these satellites come in sight in the zenith direction withan elevation angle more than 70 degrees. This timing comes once everyday with a 24-hour cycle.

Thus, by using a satellite represented by the satellite 90 to thecommunication satellite in FIGS. 13 to 16 showing examples of applyingthe orbit arrangement described above to specific systems, it will beappreciated that a communication system without communication blackoutdue to shielding and/or the presence of an obstacle can be realized.

The above example describes Case 3 in Table 4. Similarly for Case 2 inTable 4, by using an orbit arrangement in which the right ascensions ofthe north-bound node of the individual orbits are shifted by 90 degrees,either of the satellites can come in sight one after another always inthe zenith direction with its elevation angle more than 70 degrees fromthe area of the Japanese territory excluding isolated southern islands,like Okinotori Island and Minamitori Island.

(4-3) Orbit Arrangement Example 3

In this embodiment, an example of an orbit arrangement is directed toservices covering world-wide areas located between a north latitude ofapproximately 70 degrees and a south latitude of approximately 70degrees.

In this example of orbit-related elements, orbits and satellites areselected in response to the latitude of the target service area. For theservice areas located from a north latitude of approximately 70 degreesto a north latitude of 30 degrees, six orbital planes are arranged sothat their right ascensions of the north-bound node may be shifted by 60degrees, each orbital plane being formed so that the orbit cycle is 24hours, the eccentricity squared is between 0.42 and 0.48, the orbitalinclination angle is between 62 degrees and 66 degrees or between 114degrees and 118 degrees, and the argument of perigee is 270 degrees, anda couple of satellites are arranged on the individual orbital planes.With respect to the relative position of two satellites on an identicalorbital plane, one satellite is located on the perigee while the othersatellite is located on the apogee. For the service areas located from anorth latitude of 30 degrees to a south latitude of 30 degrees, 12geostationary satellites are arranged on a geostationary orbit withtheir stationary positions shifted by 30 degrees in the longitudinaldirection. In addition, for the service areas located from a southlatitude of 30 degrees to a south latitude of approximately 70 degrees,six orbital planes are arranged so that their right ascensions of thenorth-bound node may be shifted by 60 degrees, each orbital being planeformed so that the orbit cycle is 24 hours, the eccentricity squared isbetween 0.42 and 0.48, the orbital inclination angle is between 62degrees and 66 degrees or between 114 degrees and 118 degrees, and theargument of perigee is 90 degrees, and a couple of satellites arearranged on the individual orbital planes. With respect to the relativeposition of two satellites on an identical orbital plane, also in thiscase, one satellite is located on the perigee while the other satelliteis located on the apogee. The six orbital planes covering a service areafrom a north latitude of approximately 70 degrees to a north latitude of30 degrees, and the six orbital planes covering a service area from asouth latitude of 30 degrees to a south latitude of approximately 70degrees share common orbital planes. A couple of satellites with theirperigee located above the Southern Hemisphere, and a couple ofsatellites with their perigee located above the Northern Hemispheretravel on a single orbital plane, and six orbital planes so configuredwith satellites as described above exist with their orbit centersshifted by 60 degrees and around the center of the earth.

This orbit arrangement is obtained by the algorithm shown in FIG. 1, itsorbit-related elements being shown in Table 4, as realized by thecontrol method shown in FIG. 2. Owing to such an orbit arrangement andsatellite arrangement, at the areas from a north latitude ofapproximately 70 degrees to a south latitude of approximately 70degrees, at least one of 36 satellites described above can come in sightdefinitely in the zenith direction with its elevation angle more than 50degrees. At the areas from a latitude of approximately 70 degrees to alatitude of 30 degrees, in north and south bound directions, as four orsix satellites orbiting on adjacent orbital planes come in sightalternately in the zenith direction, communication lines to and from thesatellites can be established continuously. As geostationary satellitesare used at the areas from a north latitude of 30 degrees to a southlatitude of 30 degrees, a satellite can always come in sight in adefinite direction, and ultimately, stable communication can beavailable.

As described above, by using a satellite represented by the satellite 90to the communication satellite in FIGS. 13 to 16 showing examples ofapplying the orbit arrangement described above to specific systems, itwill be appreciated that a communication system without communicationblackout due to shielding and/or the presence of an obstacle can beattained.

(4-4) Orbit Arrangement Example 4

In this embodiment, an example of the orbit arrangement is directed toservices covering world-wide areas located between a north latitude ofapproximately 85 degrees and a south latitude of approximately 85degrees.

In this example of orbit-related elements, orbits and satellites areselected in response to the latitude of the target service area. For theservice areas located from a north latitude of approximately 85 degreesto a north latitude of 30 degrees, four orbital planes are arranged sothat their right ascensions of the north-bound node may be shifted by 90degrees, each orbital plane being formed so that the orbit cycle is 24hours, the eccentricity squared is between 0.42 and 0.48, the orbitalinclination angle is between 62 degrees and 66 degrees or between 114degrees and 118 degrees, and the argument of perigee is 270 degrees, andthree satellites are arranged on individual orbital planes with respectto the relative position of three satellites on an identical orbitalplane, the time for the individual satellite passing at the perigee isshifted by about 8 hours on the orbit. For the service areas locatedfrom a north latitude of 30 degrees to a south latitude of 30 degrees,12 geostationary satellites are arranged on a geostationary orbit withtheir stationary positions shifted by 30 degrees in the longitudinaldirection. In addition, for the service areas located from a southlatitude of 30 degrees to a south latitude of approximately 85 degrees,four orbital planes are arranged so that their right ascensions of thenorth-bound node may be shifted by 90 degrees, each orbital plane beingformed so that the orbit cycle is 24 hours, the eccentricity squared isbetween 0.42 and 0.48, the orbital inclination angle is between 62degrees and 66 degrees or between 114 degrees and 118 degrees, and theargument of perigee is 90 degrees, and three satellites are arranged onthe individual orbital planes. With respect to the relative position oftwo satellites on an identical orbital plane, the time for theindividual satellite passing at the perigee is shifted by about 8 hourson the orbit. The four orbital planes covering a service area from anorth latitude of approximately 85 degrees to a north latitude of 30degrees, and the four orbital planes covering a service area from asouth latitude of approximately 85 degrees to a south latitude of 30degrees share common orbital planes. Three satellites with their perigeelocated above the Southern Hemisphere, and three satellites with theirperigee located above the Northern Hemisphere travel on a single orbitalplane, and this kind of orbital plane, so configured with satellites asdescribed above, exists with its orbit center shifted by 60 degrees andaround the center of the earth.

This orbit arrangement is obtained by the algorithm shown in FIG. 1, itsorbit-related elements being shown in Table 4, as realized by thecontrol method shown in FIG. 2. Owing to such orbit arrangement andsatellite arrangement, at the areas from a north latitude ofapproximately 85 degrees to a south latitude of approximately 85degrees, at feast one of 36 satellites described above can come in sightdefinitely in the zenith direction with its elevation angle more than 50degrees. At the areas from a latitude of approximately 85 degrees to alatitude of 30 degrees, in north and south bound directions, as thesatellites orbiting on the adjacent orbital planes come in sightalternately in the zenith direction, communication lines to and from thesatellites can be established continuously. As geostationary satellitesare used at the areas from a north latitude of 30 degrees to a southlatitude of 30 degrees, a satellite can always come in sight in adefinite direction, and ultimately, stable communication can beattained.

According to the above described examples of orbit arrangement,satellite communication systems or earth observing systems in which atleast one satellite can come in sight within a circular cone formed witha tolerable semi-vertical angle extended in the central axis to thezenith can be configured with the lowest number of satellites.

In comparison with global communication systems using another middle orhigh attitude satellite, the number of satellites required for thesystem according to the present invention can be reduced. For example,in the above orbit arrangement example 1, communication lines can beestablished continuously with at least two satellites. Since the costincluding R&D, launching and operations can be reduced due to the lessnumber of satellites, the overall cost required for total systemconstruction can be reduced. Thus, ultimately, low-cost communicationservices can be provided.

(4-5) Orbit Arrangement Example 5

In this embodiment, an example of orbit arrangement is directed toservices covering the whole Japanese territory.

In the example of such an orbit arrangement, there are four orbit planesas shown in FIG. 12, and the satellite 120 a, the satellite 120 b, thesatellite 120 c and the satellite 120 d are arranged on separate orbits,respectively. The satellite 120 a travels on the orbit 121 a, thesatellite 120 b travels on the orbit 121 b, the satellite 120 c travelson the orbit 121 c and the satellite 120 d travels on the orbit 121 d,each satellite completing an orbit once in about 24 hours. The orbitcycle of the satellites 120 a, 120 b, 120 c and 120 d is about 24hours,their eccentricity squared ranges between 0.24 and 0.38, theirorbital inclination angle ranges between 35 degrees and 40 degrees orbetween 140 degrees and 145 degrees, and their argument of perigee is270 degrees. As shown in FIG. 12, their right ascensions of thenorth-bound node shift mutually by 90 degrees, and are defined so thattheir apogees may be located at a desired position above the Japaneseterritory.

In terms of relative position between the satellites on their ownorbits, when the satellite 120 a is located at the perigee on the orbits121 a, the satellite 120 b and the satellite 120 d are arranged to beshifted by 122.5 degrees from the apogee on their corresponding orbits121 b and 121 d, respectively, and the satellite 120 c is arranged to belocated at the apogee on its corresponding orbit 121 c.

With such an orbit arrangement, at the areas in Hokkaido, Honshu,Shikoku and Kyuhu and Okinawa, the satellite 120 a, the satellite 120 b,the satellite 120 c or the satellite 120 d can come in sight always inthe zenith direction with its elevation angle more than 70 degrees. Asthe satellite 120 a, the satellite 120 b, the satellite 120 c and thesatellite 120 d have a 24-hour orbit cycle, the occurrence of in-sightand out-of-sight positions of the satellite in the zenith direction withits elevation angle more than 70 degrees is periodic and orderly.

This orbit arrangement is obtained by the algorithm shown in FIG. 1,realized by the control method shown in FIG. 2. In this case, thesatellite 120 a, the satellite 120 b, the satellite 120 c and thesatellite 120 d alternately come in sight and out of sight onceeveryday, and their duration time for in-sight positions in the zenithdirection with its elevation angle more than 70 degrees is about 6hours.

Thus, either of those satellites can come in sighs one after another allday long for 24 hours in the zenith direction with its elevation anglemore than 70 degrees. There exists certainly a timing when all of thesesatellites come in sight in the zenith direction with an elevation anglemore than 70 degrees. This timing comes once every day with a 24-hourcycle.

Thus, by using a satellite represented by the satellite 90 to thecommunication satellite in FIGS. 13 to 16 showing examples of applyingthe orbit arrangement described above to specific systems, it will beappreciated that a communication system without communication blackoutdue to shielding and/or the presence of an obstacle can be attained.

In the Orbit Arrangement Example 1 described above, what is shown is anexample in which either of two satellites can come in sight one afteranother all day long for 24 hours in the zenith direction with itselevation angle more than 55 degrees. In contrast, in the OrbitArrangement Example 5 using 4 satellites, any of those satellites cancome in sight one after another all day long for 24 hours in the zenithdirection with its elevation angle more than 70 degrees. Tables 8, 9 and10 show the occurrence of in-sight and out-of-sight positions ofsatellites from 10 cities in Japan.

TABLE 8

TABLE 9

TABLE 10

In Tables 8 to 10, terms “Ambsat-1” to “Ambsat-4” representidentification codes for the individual satellites. In those tables, thefine line represents the time period for which the satellite is insight, with its elevation angle more than 55 degrees, from theindividual city, and the thick line including the fine line representsthe time period for which the satellite is in sight, with its elevationangle more than 80 degrees, from the individual city.

According to this orbit arrangement example, in the area from Sendaidown to Osaka, any of the satellites can come in sight in the zenithdirection with its elevation angle more than 80 degrees for a timeperiod of more than 80% of a 24-hour day.

(5) Systems using Satellites Traveling on Orbits in Accordance with thePresent Invention

(5-1) System Example 1

System Example 1 is a satellite communication system covering thecommunication services in the whole Japanese territory, and FIG. 13shows an example of a Mobile Communication Phone System.

As shown in FIG. 13, this system is composed of an artificial satellite90 having an attitude control subsystem suitable for the above mentionedelliptic orbits, a power supply subsystem, a communication subsystem anda thermal control subsystem, a ground mobile communication terminal 91making it possible to perform satellite communication via the artificialsatellite 90, a fixed phone terminal 92, a fixed phone network 93, acellular phone terminal 95, a cellular phone network 95 and a gatewaycommunication station 94.

The ground mobile communication terminal 91 enables communication withfixed phone terminals 92 and/or cellular phone terminals 95. In the casein which the ground mobile communication terminal 91 is used within atarget service area which is characterized by one of the inputconditions for defining six orbit-related elements of the satellites inaccordance with the present invention, the ground mobile communicationterminal 91 has a send/receive means for sending and receiving signalswith the satellite 90 coming in sight within a predetermined range ofelevation angle extended in the zenith direction. With thisconfiguration, for example, in case of using a directional antenna as asend/receive means in the ground mobile communication terminal 91, theuser does not need to search for the direction (north, south, east orwest) in which the satellite can be reached, but only directs theantenna in the zenith direction wherever he or she may be in the servicearea.

According to this system example, global-scale mobile communicationservices, such as cellular phone and car phone services, can beprovided. As global-scale communication systems can be configured with asmaller number of satellites, low-cost communication services can beprovided.

(5-2) System Example 2

System Example 2 is a satellite communication system directed todomestic service covering the whole Japanese territory, and FIG. 14shows an example of image transfer system for vehicles, such as anambulance.

As shown in FIG. 14, this system is composed of an artificial satellite90 having an attitude control subsystem suitable for maintaining theabove mentioned elliptic orbits, including a power supply subsystem, acommunication subsystem and a thermal control subsystem, an ambulance 97and a critical care center 98. The image data 99 produced by anendoscope, a sonagram an electrocardiogram and a camera used foremergency cases carried by the ambulance 97 are transferred to thecritical care center 98 via satellite 90, and some feedback information100 related to emergency treatment suitable for the emergency cases canbe transferred from the critical care center 98. Though an ambulance ina paramedic system is taken to be an example of the mobile environmenthere, another system similar to this example can be applied to the casesin which a large amount of date may be transferred from and to a movablebody.

According to this system, since at least one satellite will come insight within a circular cone with its semi-vertical angle extended inthe central axis to the zenith, stable communication lines can be easilyestablished for a long period of time by using the satellite accordingto the present invention, even in such an area in which the field ofvision may be blocked by artificial building structures, plants andnatural topographic features. With this system, image data transfer frommovable bodies, such as ambulance and an outside broadcast van, forrelay from the spot can be made available almost on a full-time basiswithout influence by environmental obstructions. In addition, accordingto this example, as image data related to emergency cases aretransferred from the ambulance to the critical care center and feedbackinformation related to emergency treatment suitable for the emergencycases can be obtained within the moving ambulance, suitable treatmentcan be applied to the emergency cases while carrying a patient to thecritical care center. Thus, it will be appreciated that the life of theemergency case may be saved if suitable treatment could be madeavailable to the emergency case while carrying a patient to the criticalcare center. This system also can be applied to TV systems forbroadcasting sports events, in which high quality images can betransferred in real time.

(5-3) System Example 3

System Example 3 is a satellite communication system directed to adomestic service covering the whole Japanese territory, and FIG. 15shows an example of a rescue support system for mountain and/or oceanareas.

As shown in FIG. 15, this system is composed of an artificial satellite90 having an attitude control subsystem suitable for maintaining theabove mentioned elliptic orbits, including a power supply subsystem, acommunication subsystem and a thermal control subsystem, an artificialsatellite 102 forming an global earth observing system, a mobilecommunication terminal 107 which makes it possible to measure thelocation of the person in trouble by measurement signals from the globalearth observing system and to communicate via satellite 90, and amountain rescue center 105 located in police and/or fire stations. Aclimber in distress 101 on a mountain can identify his or her locationby using the mobile communication terminal 107 while receiving theposition signal 103 from the satellite 102 forming a part of the globalearth observing system, and can transfer data 104 including his or herposition, ID, and number of accompanying persons, to the mountain rescuecenter 105 in the police and/or fire stations via satellite 90. Inresponding to such data, the mountain rescue center initiates rescueoperations. In this case, if a rescue helicopter 106 is available, bytransferring the data 104 to the rescue helicopter 106, rescueoperations can be developed more rapidly. In this case, an applicationof the system to the rescue of mountain climbers is merely one example,since this system can be applied to rescue the of anyone, such as peoplelost at sea.

According to this example, a person in distress on a mountain or in theocean can identify his or her position and transmit it to a rescuecenter via satellites. Conventionally, in order to search for people indistress on mountains, a rescue team searches for the person in distressby using many helicopters and/or walking through mountains. By usingthis system, since it is possible to identify the position of people indistress in advance, the activity of the rescue team can be optimizedand a prompt rescue operation can be developed.

(5-4) System Example 4

System Example 4 is a satellite communication system directed to adomestic service covering the whole Japanese territory, and FIG. 16shows an example of an automated accounting system for public utilitycharges.

As shown in FIG. 16, this system is composed of an artificial satellite90 having an attitude control subsystem suitable for maintaining theabove mentioned elliptic orbits, including a power supply subsystem, acommunication subsystem and a thermal control subsystem, an artificialsatellite 102 forming a global earth observing system, a public utilitycharge accounting center 108, a fixed communication terminal 109 whichmakes it possible to communicate vie satellite 90 and terminals 109 a,109 b, 109 c and 109 d for measuring the consumption of electricity, gasand water. The fixed communication terminal 109 and the measurementterminals 109 a, 109 b, 109 c and 109 d for measuring the consumption ofelectricity, gas and water are installed in individual houses, multipledwelling houses and large buildings. Those terminals measure the amountof consumption and transfer the measured data periodically to the publicutility charge accounting center 108 via satellite 90. With this system,conventional and human-intensive door-to-door efforts for reading metersfor electricity, gas and water supply can be automated efficiently, anda billing operation for all the public utility charges can be processed.

In this system, by using the satellites traveling on the orbits inaccordance with the present invention, satellite communication lines canbe easily established even with an antenna facility located on a lowerbuilding surrounded by high-rise buildings. By applying this system,public utility charges which are now processed with conventional andhuman-intensive door-to-door efforts for reading meters for electricity,gas and water can be accounted via satellite, and a labor cost requiredfor reading meters can be reduced to a large extent, which, ultimately,will be expected to cut public utility charges.

In the system examples 1 to 4, though the satellite 90 in FIGS. 13 to 16is shown as a single satellite, this illustration of a satellite isrepresentative of plural satellites. The artificial satellite 102 isalso representative of Navstar satellites forming a Global PositioningSystem (GPS) of USA, GLONASS satellites for a navigation system,multi-purpose transportation satellites of Japan and so on.

(5-5) System Example 5

FIG. 17 shows an example of a system configuration of a satellitecommunication mobile station mounted on the ambulance 97 shown in FIG.14.

This system is used for transferring normal-quality dynamic pictureimages, high-quality dynamic or static picture images, medicalinspection data related to the status of an emergency case, and forreceiving medical treatment directions from the critical care center 98operated as a base station for the communication system, through stabledata transfer lines established by using satellites located in thedirection of high-elevation angles so as to be not influenced by themoving location and communication condition of the ambulance 97.

This system has the following means as components used for exchangingdata via satellite: send/receive antenna 201, electric power amplifier202, frequency converter 203, modulator 204, camera 205, microphone 206,image compression and encoding apparatus 207, access telephone 208, lownoise amplifier 212, frequency converter 213 and demodulator 214.

In addition, this system has the following means for attitude control ofthe send/receive antenna 201 mounted on the moving ambulance 97: Beaconreceiver 217, antenna controller 216, motor driver 215, elevation anglecontrol motor 209, polarization angle control motor 210 and azimuthalangle control motor 211.

And furthermore, this system has the following means as components forsupplying supplementary data used for optimizing means for attitudecontrol of the send/receive antenna: accelerometer 224, gyroscope 225,GPS antenna 218, VICS antenna 220, GPS receiver 219, VICS receiver 221and image display apparatus 222.

In this system, the EMT (emergency medical technician) on board theambulance can have a conversation with a duty doctor at the criticalcare center 98 by using access telephone 208 via satellite 90. Image andvoice information related to the physical condition of the emergencycase are obtained by the access telephone 208, the camera 205 and themicrophone 206, and are processed for image compression and encoding bythe image compression and coding apparatus 207, and then, modulated bythe modulator 204, and next, multiplied by the electric power amplifier202, and finally, sent from the send/receive antenna 201 to thesatellite 90.

The information received by the satellite 90 is transferred from thesatellite 90 to the critical care center 98. At the critical care center98, the duty doctors examine the data related to the emergency case andsend directions for suitable medical treatment to the ambulance 97 viasatellite 90.

The information for medical treatment for the emergency case is receivedby the send/receive antenna 210 mounted on the ambulance 97, and afterbeing amplified by the low noise amplifier 212, frequency conversion iseffected using the frequency converter 213, and then, the processedsignal is demodulated by the demodulator 214 and forwarded to the accesstelephone, with which the EMT can receive the directions for the medicaltreatment issued by the duty doctors at the critical care center.

The intensity of the signal received by the send/receive antenna 201 isoptimized by driving the elevation angle control motor 209, thepolarization angle control motor 210 and the azimuthal angle controlmotor 211 with the motor driver 215 responding to the signal from theantenna controller 216, and changing the direction of the send/receiveantenna 201 so that the intensity of the Beacon signal separated by thefrequency converter 213 and received by the Beacon receiver may beoptimized.

When changing the direction of the antenna, it is possible to use, asone parameter for optimization, the position signal received from GPSsatellite forming the global earth observing system by GPS antenna 218and GPS receiver 219. In addition, by detecting the change in the movingdirection of the ambulance using the accelerometer 224 and the gyroscope225 and configuring the system so as to supply supplementary data forattitude control for the antenna, it is possible to configure the systemto establish high-adaptability in the attitude control of the antenna.

The route selection of the ambulance can be supported with GPS receiver219 and GPS antenna 218, and also with information supplied by VICSantenna 220 and VICS receiver 221.

(5-6) System Example 6

System Example 6 is a satellite communication system directed to adomestic service covering the whole Japanese territory, and FIG. 18shows an example of a program in a system having plural movable bodies.

As shown in FIG. 18, this system is composed of an artificial satellite232 having an attitude control subsystem suitable for the abovementioned elliptic orbits, a power supply subsystem, a communicationsubsystem and a thermal control subsystem, a satellite communicationground station 231 for supplying programs to plural movable bodies, anartificial satellite 233 forming a global earth observing system,movable bodies 235 used for public transportation, such as a taxi and arailway vehicle, movable bodies 236 used for private transportation,such as an owner-driver car, and a master station 234 for sending VICSinformation. In this system, communication system devices to bedescribed in FIG. 19 are loaded on the movable bodies 235 and 236.

GPS antenna 256 and GPS receiver 257 are loaded on the movable bodies235 and 236, respectively, which receive position signals from theartificial satellite 233 forming a global earth observing system andoperate to measure its own position, attitude and velocity, and send themeasured information back to the send/receive terminal 244. The movablebodies 235 and 236 have a receiving antenna 257 and VICS receiver 259,which receive signals from a VICS information base station, and performa function for receiving traffic jam information, the receivedinformation being forwarded similarly to the send/receive terminal 244.The send/receive terminal 244 accepts operation commands supplied by thesystem user for selecting his or her desired information from availableinformation, and collects the selected information.

The information obtained by GPS receiver 258, the information obtainedby VICS receiver 259 and the collected information selected by thesystem user is processed in the send/receive terminal 244, and is nextmodulated by the modulator 243, then processed by the frequencyconverter 242, and after the processed signal is amplified by the poweramplifier 241, the amplified signal is sent to the satellite 232 fromthe send/receive antenna 240.

This transmitted signal is transferred to the satellite communicationbase station 231 of the program supplier via satellite 232. In thesatellite communication base station 231, according to the informationtransmitted from the movable bodies 235 and 236, the programs suitablefor the location, time zone and user's request, while those movablebodies move, are distributed to the movable bodies 235 and 236 viasatellite 232.

In accordance with the present invention, the classes of programs to bedistributed are not limited. According to the present invention, sincethe satellite 232 can be located at a higher elevation angle, stable andcontinuous transmission lines via satellite 232 can be establishedwithout being influenced by the moving status of the movable bodies.Therefore, dynamic picture images, static picture images and teletextcan be received. As some specific class of programs may requiresadditional signal processing methods and devices, like frame memories,necessary modification and extension for the system configuration are tobe considered.

As for programs to be distributed, for example, there are discount salesinformation from department stores and supermarts, exhibitionannouncements from art galleries and museums, cinema programs from movietheaters, criminal suspects and missing persons information, andInternet information.

The movable bodies 235 and 236 receive the information sent viasatellite 232 from the satellite communication base station 231 of theprogram supplier via the send/receive antenna 240 mounted thereon. Thereceived signals are amplified by the low noise amplifier 248, and thenprocessed by the frequency converter 249, and after being modulated bythe modulator 247, the video information is displayed on the imagedisplay device 245 and the audio information is output from the speaker246.

The modulated signal supplied from the modulator 247 contains theprogram information to be selected on the basis of local areas in whichthe movable bodies move, and this information can be recognized as videoand/or audio information from the image display device 245 and/or thespeaker 246, as well as being forwarded to the send/receive terminal244.

The intensity of the signal received by the send/receive antenna 240 isoptimized by driving the elevation angle control motor 253, thepolarization angle control motor 254 and the azimuthal angle controlmotor 255 with the motor driver 252 responding to the signal from theantenna controller 251, and by changing the direction of thesend/receive antenna 240 so that the intensity of the Beacon signalseparated by the frequency converter 249 and received by the Beaconreceiver may be optimized.

According to this system, the information suitable for a designatedlocation in an urban area can be definitely transferred to the movablebody. If the conventional {rv set is loaded on the movable body and TVsignals from the ground station or the geostationary satellite arereceived using a conventional method, the TV programs can not becontinuously and stably enjoyed on the movable bodies because of theinfluence of building structures and trees which may block the TVsignals. However, in the transmission and communication lines of thissystem, TV signals come from the upper air in the zenith direction.Therefore, TV signals are not influenced so much by building structuresand trees, and TV programs can be enjoyed stably.

In addition, according to this system, as department stores andsupermarts can distribute discount sales information in a timely mannerto the movable bodies moving in the neighboring areas of the stores, itwill be appreciated that the stores may expect to bring in morecustomers.

In addition, by providing information related to criminal suspects andmissing persons with photos transmitted to the movable bodies, it willbe appreciated that criminal suspects and missing persons may be foundearlier than expected.

The above described system examples 1 to 6 assume that the targetservice area provided by the satellite on the elliptical orbit inaccordance with the present invention is the whole Japan territory, andthat the services may be available when the elevation angle of thesatellite as viewed from the location in the target service area becomeshigher. However, the present invention is not limited to this case. Forexample, in case the elevation angle of the satellite viewed from thelocation in the target service area becomes lower, the followingapplications can be considered.

In response to the trajectory of the elliptical orbit of the satellite,in case the elevation angle of the satellite as viewed from the locationin the target service area becomes lower, the communication servicebetween the locations outside the target service area and the locationsinside the target service area can be relayed. In case the elevationangle becomes much lower, the communication service between other areasoutside the target service area can be relayed.

(6) Satellite Orbit Control System Example

The orbit of the above described satellites is controlled in thefollowing manner.

Six orbit-related elements suitable for the target service area obtainedby the algorithm shown in FIG. 1 (semi-major axis 11, perigee argument12, eccentricity squared 13, orbital inclination angle 14, rightascension of north-bound node 15 and true anomaly 16) are put into thelauncher operation control facility 21 as target orbit parameters asshown in FIG. 2. This information is transferred from the launcheroperation control facility 21 to the launcher 23 in order to launch thesatellite 20 onto the target orbit. In case the launcher 23 loaded withthe satellite 20 happens to stray off the target orbit during thelaunching operation, it is possible for the launcher 23 itself tocorrect its orbit or it is possible for the launcher operation controlfacility 21 to send the operation command for correcting the orbit tothe launcher 23 and navigate the launcher.

Even after the satellite reaches the target orbit having the targetorbit-related elements 22, the orbit-related elements will be perturbedby the influence of the earth's gravitational field, the attractiveforce produced by the Moon and the Sun and solar wind, and so theorbit-related elements change all the time in a short cycle or a longcycle. In such a case, the satellite 20 requires an orbit control.

As shown in FIG. 3, six orbit-related elements 31 of the orbit on whichthe satellite 20 travels are determined by the following steps:telemetry ranging signals 27 transmitted by the satellite 20 arereceived by the send and receive system 24 of the satellite operationcontrol facility 18, ranging signals 28 are extracted and forwarded tothe range measurement system, and a measured range and its rate ofchange 29 are used as input data and processed by the orbitdetermination program 30 in the computer system 26. By comparing the sixorbit-related elements 31 obtained in this manner and the sixorbit-related elements 17 suitable for the target service area asreference values, the orbit control program 32 in the computer system 26calculates necessary attitude control values and orbit control values33. Finally, which thrustor of the propulsion system of the satelliteshould be driven and how long this drive operation should last can bedetermined. Those results are converted into the control command 35 bythe command generation program 34 in the computer system 26 and aretransferred to the satellite 20 via the send and receive system 24 ofthe satellite operation control facility 18.

As shown in FIG. 4, the control command transferred to the satellite 20is received by the communication system 37 loaded on the satellite 20and the transferred command is interpreted by the data processing system38. In response to the interpreted command, information related to thealtitude control variable and the orbit control variable is processed bythe attitude/orbit control system 39 loaded on the satellite. Ifnecessary, by means of a change in the attitude of the satelliteproduced by driving the attitude control actuator 42, the thrustor ofthe propulsion system 40 loaded on the satellite being driven inresponse to the control command, the satellite 20 is finally controlledso as to trace the orbit defined by six orbit-related elements 17suitable for the target service area. In addition, in case the satellite20 has a receiver for GPS (Global Positioning System) or GLONASS formingthe global earth observing system on board, the system may be configuredso that the satellite 20 itself stores six orbit-related elements 17suitable for the target service area and the satellite may control itsorbit trajectory autonomously by using the stored parameters.

As described above, the orbit-related elements 17 suitable for thetarget service area determined by the algorithm shown in FIG. 1 iscontrolled and realized.

According to the present invention, a method for setting an orbit of thesatellite required for the satellite to come in sight in the zenithdirection over an extended time period and six orbit-related elements todefine the orbit, and various systems for using the satellite travelingon this orbit can be provided.

In addition, according to the present invention, an orbit control systemis provided for realizing orbit control of the satellite based on thesix orbit-related elements so defined in the above described manner.

What is claimed is:
 1. A communication terminal for communicatingthrough an artificial satellite, wherein said artificial satellite isplaced into an orbit in which an individual satellite orbits on anelliptical orbit so that at least one of the artificial satellites isalways viewable within a pre-defined range of operational elevationalangle in a zenith direction from a service area; a group of saidartificial satellites are satellites on respective orbits obtained bycombining an inclination angle and an eccentricity squared of saidelliptical orbit so that a time period during which an artificialsatellite is viewable from ground is substantially identical; and saidcommunication terminal has a transmitting and receiving means fortransmitting and receiving a signal through said group of artificialsatellites.
 2. A communication terminal of claim 1 used in combinationwith a telephone terminal or a telephone network.
 3. A communicationterminal having a transmitting and receiving means for transmitting andreceiving a signal through an artificial satellite, wherein saidcommunication terminal further comprises a measuring means for receivinga radio wave from a GPS satellite and measuring at least its position aswell as a means for transmitting and receiving a signal through saidartificial satellite; said artificial satellite is placed into anorbit,in which an individual satellite orbits on an elliptical orbit sothat at least one of the artificial satellites is always viewable withina pre-defined range of operational elevational angle in a zenithdirection from a service area; and a group of said artificial satellitesare satellites on respective orbits obtained by combining an inclinationangle and an eccentricity squared of said elliptical orbit so that atime period during which an artificial satellite is viewable from groundis substantially identical.
 4. A communication terminal having atransmitting and receiving means for transmitting and receiving a signalthrough an artificial satellite, wherein said communication terminalfurther comprises a measuring means for measuring at least one ofquantity consumed to be charged as electricity, gas or public watersupply; said artificial satellite is placed into an orbit in which anindividual satellite orbits on an elliptical orbit so that at least oneof the artificial satellites is always viewable within a pre-definedrange of operational elevational angle in a zenith direction from aservice area; and a group of said artificial satellites are satelliteson respective orbits obtained by combining an inclination angle and aneccentricity squared of said elliptical orbit so that a time periodduring which an artificial satellite is viewable from ground issubstantially identical.
 5. A ground-based station for receiving aobservatory result transmitted from an satellite having an earthobservatory equipment, wherein said artificial satellite is placed intoan orbit in which an individual satellite orbits on an elliptical orbitso that at least one of the artificial satellites is always viewablewithin a pre-defined range of operational elevational angle in a zenithdirection from a service area; and a group of said artificial satellitesare satellites on respective orbits obtained by combining an inclinationangle and an eccentricity squared of said elliptical orbit so that atime period during which an artificial satellite is viewable from groundis substantially identical.
 6. A moving body having a communicationterminal with a transmitting and receiving means for transmitting andreceiving a signal through an artificial satellite and moving mainly ina service area, wherein said artificial satellite is placed into anorbit in which an individual satellite orbits on an elliptical orbit sothat at least one of the artificial satellites is always viewable withina pre-defined range of operational elevational angle in a zenithdirection from a service area; and a group of said artificial satellitesare satellites on respective orbits obtained by combining an inclinationangle and an eccentricity squared of said elliptical orbit so that atime period during which an artificial satellite is viewable from groundis substantially identical.
 7. A moving body having a satellitecommunication terminal with a transmitting and receiving means fortransmitting and receiving a signal through an artificial satellite andmoving mainly in a service area, wherein said artificial satellite isplaced into an orbit in which an individual satellite orbits on anelliptical orbit so that at least one of the artificial satellites isalways viewable within a pre-defined range of operational elevationalangle in a zenith direction from a service area; and a group of saidartificial satellites are satellites on respective orbits obtained bycombining an inclination angle and an eccentricity squared of saidelliptical orbit so that a time period during which an artificialsatellite is viewable from ground is substantially identical.
 8. Aground-based station for communicating with a satellite communicationterminal, wherein an artificial satellite is placed into an orbit inwhich an individual satellite orbits on an elliptical orbit so that atleast one of the artificial satellites is always viewable within apre-defined range of operational elevational angle in a zenith directionfrom a service area; a group of said artificial satellites aresatellites on respective orbits obtained by combining an inclinationangle and an eccentricity squared of said elliptical orbit so that atime period during which an artificial satellite is viewable from groundis substantially identical; and said ground-based station has at least areceiving means for receiving an information containing at least animage information captured during a moving operation of a moving bodyhaving said satellite communication terminal before its moving actionand transmitted from said satellite communication terminal through saidgroup of artificial satellites; a display means for displaying an imageinformation contained in an information received said receiving means;and a transmitting means for transmitting an information to be receivedby said artificial communication terminal during a moving operation ofsaid moving body.